(a) Field of the Invention
The present invention relates to a zoom lens system and, more particularly, to a zoom lens system comprising four lens group and having comparatively simple lens configuration.
(b) Description of the Prior Art
There are known zoom lens systems comprising four lens groups, i.e., a first, second, third and fourth lens groups, in which the first, second and third lens groups constitute a varifocal subsystem, the first lens group being a focusing lens group and having positive refractive power, the second lens group being a variator and having negative refractive power, the third lens group being a compensator and having positive refractive power, the fourth lens group being a relay lens arranged in rear of the varifocal subsystem. Among known zoom lens systems comprising four lens groups as described in the above, there are such known zoom lens systems in which the fourth lens group, i.e., the relay lens, is arranged to have simplified lens configuration in order to simplify the lens configuration of the lens system as a whole. Japanese published unexamined patent application No. 126819/81 discloses an example of known zoom lens systems in which the relay lens is arranged to have simplified lens configuration as described in the above. The relay lens of the known zoom lens system disclosed in the abovementioned Japanese published unexamined patent application comprises a lens component, which comprises a positive lens and negative lens arranged in the order from the object side (varifocal subsystem side) and has positive refractive power as a whole, a biconvex lens arranged by leaving a comparatively large airspace in respect to said lens component, and a negative meniscus lens arranged to be convex toward the image side. The relay lens of said known zoom lens system has a disadvantage that positive distortion caused by the negative meniscus lens, which is arranged on the image side, cannot be satisfactorily corrected on the long focal length side.
Another example of the above-mentioned known zoom lens systems is disclosed in Japanese published unexamined patent application No. 131852/78. The relay lens of the known zoom lens system disclosed in the above-mentioned Japanese published unexamined patent application comprises a lens component, which comprises a positive lens and negative lens and has positive refractive power as a whole, a negative meniscus lens arranged by leaving a comparatively large airspace in respect to said lens component and arranged to be convex toward the image side, and a positive lens. Said zoom lens system has a disadvantage that coma caused by the negative meniscus lens is large because the converging action in the position in rear of the relay lens is insufficient and, therefore, it is difficult to obtain favourable contrast of image.